Add ca-certificates to Dockerfile.hsm

This addition is necessary if you want to run the smallstep/step-ca:hsm
container in linked mode. Without ca-certificates, the container is
unable to verify https certificates of and connect to smallstep.com

docker/Dockerfile.hsm

@@ -18,7 +18,8 @@ COPY --from=kms /usr/local/bin/step-kms-plugin /usr/local/bin/step-kms-plugin
 
 USER root
 RUN apt-get update
-RUN apt-get install -y --no-install-recommends pcscd libpcsclite1
+RUN apt-get install -y --no-install-recommends pcscd libpcsclite1 ca-certificates
+RUN update-ca-certificates
 RUN mkdir -p /run/pcscd
 RUN chown step:step /run/pcscd
 USER step